Hi @Smil-ey ,
Per my knowledge, if we open the document in a browser, there are a lot of functional limitations.
As mentioned in this article, online editing does not support send a digital signature and encryption,you need to use these more features in desktop applications:
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Regarding the second question, we want to confirm:
- Does "Not secure" appear only when the document is opened, and not at other times?
- What browser are you using? You could try to use other browsers to see if it works normally.
- Usually, if the http protocol is used, similar insecure prompts may appear. You can check whether the url uses http:// or https://.
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